Composition, pressure, and temperature of the mantle source region of quaternary nepheline-basanitic lavas in Bitlis Massif, Eastern Anatolia, Turkey: A consequence of melts from Arabian lithospheric mantle

摘要

The Quaternary (0.66-0.63 Ma) nepheline basanites (ne - basanite) are the firstly observed volcanic products of Arabia-Eurasia collision on Bitlis Pottirge Massif. They composed of clinopyroxene, olivine, Ti-magnetite, Cr spinel, and nepheline. The forsterite compositions of olivines range between 73 and 83%, calcic clinopyroxenes show modest variations in Wo(48-57)-En(37-45)-FS5-7 and nephelines occur as minor minerals within the networks of other groundmass minerals. They are characterized by low SiO2 (40.16-41.96 wt%), high MgO contents (8.54-9.73 wt%) and similar Sr-Nd isotopic compositions with Arabian Plate volcanics. Mineral and whole rock thermobarometry yield crystallization pressure and a temperature range between 8 and 20 kbar and 1301 degrees C - 1035 degrees C respectively. Lavas have high Mg -number (>0.58), high Cr and Ni contents and strong LREE enrichment but depletion in Rb, K, and Pb. Trace elements together with Sr isotopic compositions inferred negligible assimilation of the local upper crustal material. The calculated average pressure and temperature of mantle melting for ne-basanites is 2,85 kbar and 1353 degrees C respectively. FC3MS (wt% FeO/CaO-3*MgO/SiO2) parameter and melting models using REE data reveal catak basanites are products of amphibole and phlogopite bearing metasomatised lithospheric mantle in garnet stability field. They seem to originated from depths of similar to 85 km which corresponds to the base of the Arabian lithosphere in the region. (C) 2019 Elsevier B.V. All rights reserved.